1. Field of the Invention
The present invention is generally directed toward pump control systems and methods and, more particularly, toward a system and method for preventing a pump from running dry.
2. Description of Related Art
Many pumps, such as those used on marine vessels, have a finite supply of water. Other pumps may have their water supply interrupted because of a blockage or break in the supply-side plumbing. Unfortunately, these types of pumps are susceptible to damage from running-dry.
Traditionally, and in response to this potential danger, these types of pumps have included water pressure sensors or pump temperature sensors to turn the pump off. However, such measures may be inadequate or too slow to prevent damage to the pump.
It has also been proposed to install sensors in the pump intake conduit and to use these sensors to detect whether liquid is present in the intake conduit. For example, U.S. Pat. Nos. 3,993,945; 4,553,552; 4,357,131; and 6,122,956 all show different sensor arrangements wherein the sensor is embedded in the conduit sidewall, or projects from the conduit sidewall, and is used to detect whether liquids are present in the conduit. These patents show that embedded sensor arrangements, and using information from the embedded sensors to control a pump, are known in the art. However, these arrangements suffer from the disadvantage that the sensors are expensive to manufacture, install, and implement, and require substantial modifications to known equipment and plumbing. Moreover, the exposed sensors may be damaged during use, rendering inoperable any pump activation and shut-down system incorporating the sensors.
Therefore, there exists a need in the art for a device for sensing liquid in a conduit and a method for controlling a pump in response to sensed liquid that is reliable, inexpensive, and durable.
The present invention is directed toward a liquid sensor for sensing the presence of liquid in a conduit, and toward a pump control system that shuts down the pump in response to the signals from the liquid sensor.
In accordance with the present invention, a sensor for detecting the presence of water in a passageway communicating with a pump includes first and second conductive fittings and a third non-conductive fitting disposed between the first and second fittings. The first and second fittings have electrodes secured to their exterior surfaces. Water to be detected flows through the sensor, and electrical current flowing between the first anid second fittings is used to determine whether water is present in the sensor.
In accordance with another aspect of the invention, a pump shutdown system includes a sensor and an electrical detection device. The sensor is a flow-through sensor defining a portion of a water passageway leading toward or away from a pump to be controlled. The sensor includes a first conductive fitting, a second conductive fitting, and a third non-conductive fitting extending between and sealingly secured to the first and second conductive fittings. The sensor defines a portion of a water passageway and is in fluid communication with the pump. The first and second members have electrodes secured to their exteriors. An electronic detection device is also provided and electrically connected to the electrodes. The electronic detection device is operable to apply a voltage across the first and second conductive members and to detect a current flowing between the first and second conductive members. The electronic detection device detects a current flowing between the first and second conductive members and shuts down the pump if the detected current flow is less than a predetermined minimum.